Vue 自定义校验规则

        <el-form-item label="所属地区" prop="region">

          <el-select v-model="formParam.province" ref="province" placeholder="请选择省" clearable filterable>
            ...
          </el-select>

          <el-select v-model="formParam.city" ref="city" placeholder="请选择市" filterable clearable>
            ...
          </el-select>

          <el-select v-model="formParam.area" ref="area" placeholder="请选择区" filterable clearable>
            ...
          </el-select>

        </el-form-item>

data() {
    let checkRegion = (rule, value, callback) => {
        //自定义校验
        //this.$refs.province.value
        //this.$refs.city.value
        //this.$refs.area.value
        this.$refs.province.value ? callback() : callback(new Error('请选择省市区'))
        };

      return {
      ...
        rules: {
         ...
          region: [
            {required: true, validator: checkRegion, trigger: ["blur", "change"]},
          ],
        },
      }
    },